Remote indicating means



April 9, 1946. N. w. HARTZ REMOTE INDICATING MEANS Filed June 5, 1943 2Sheets-Sheet l 7 -N. w. HARTZ 2,397,962

REMOTE INDICAT ING MEANS April 9, 1946.

Filed June 3, 1943 2 Sheets-Sheet'Z Patented Apr. 9, 1946 UNITED STATESPATENT OFFICE 2.391.962 rumors mnrca'rmo MEANS Nelson W. Hartz,Pittsburgh, Pa. Application June 8, 1943, Serial No. 489,481

9 Claims. (Granted under the act of March 3, 1883, as

amend d April 30, 1928; 370 O. G. 757) A primary object of the presentinvention is.

to provide an improved remote indicating system of the general classdescribed wherein certain provisions are made for overcomingdisadvantages )f present systems involving instability due to vibrationfactors present in aircraft operation, interference with properoperation due to extreme variations in the temperature range to whichinstruments are subjected in aircraft operation, and other factorsmentioned more in detail hereinafter.

Remote indicating systems at present employed in aircraft fall intothree general classifications.

One classification involves the type of system in which direct pressureconnection is employed between the indicator instrument and the factordesired to be indicated. Such systems usually avail of a fluid pressuretransmitting medium through fluid conduits. These are subject tomalfunctioning at extreme temperatures or due to breaks or leakage inthe conduits.

Another classification involves the alternating current Selsyn typeremote indicating system wherein an electric motor operates theindicator at a. point remote from, and in response to, correspondingvariations in a controlling electric jmotor at the location of thefactor desired to be indicated. These systems have certain advantagesbut in general are complicated and expensive.

A third classification involves the systems utilizing an electriccircuit employing current or voltage responsive indicator means in whichthe varying physical force of the factor desired to be indicated iscaused to vary the resistance in. the circuit to produce a correspondingvariation in the current responsive indicating means at the remotelocation. The present invention relates more particularly to the latterclass of remote indicating systems.

In the latter type of system a variable resistance, comprising a slidewire rheostat or potentiometer is usually employed in conjunction with va pressure responsive means such as a piston and cylinder, Bourdon tube,or bellows to vary the contact position of the rheostat orpotentiometer. Such an instrumentality, comprising a variable resistanceand pressure responsive means for varying the same, is referred toherein as a transmitter or transmitting means. The types of suchtransmitters heretofore used involving the slide.

wire or bimetal resistance are subject to certain disadvantages peculiarto the operational conditions in remote indicating systems for use inaircraft. These operational conditions involve vibration as it aifectsinstability of electrical systems including variations in indicatorreading due to such vibration; vibration as it affects wear of thecontact member of the rheostat upon the wirewound resistance causing anuneven variation in the resistance on account of the resulting unevenpressure of the contact member with respect to the wire; friction. dueto the sliding contact and due also to congealing of the lubricant; andmalfunctioning due to the effects of temperature change. The metalresistance members are also subject to corrosion which results inmalfunctioning. These factors result in inaccurate indicator reading anduncertaintyof operation in reference to the use of this type of remoteindication system.

It is an object of the present invention to provide a remote indicatingsystem and a transmitting means for use therein, which overcome thedisadvantages above mentioned and yet which are simple in constructionand inexpensive to manufacture, positive in operation and substantiallyunaffected by vibration and temperature conditions encountered inaircraft operation.

The basic concept of the present invention involves the employment, in aremote indicating system of the class described, of a transmitting meanscomprising a variable resistance, including a liquid conductor in theelectrical telemetering circuit and means responsive to physicalconditions external to said circuit for varying the resistance thereof.In the embodiments of the invention herein'disclosed the electricaltelemetering circuit includes a source of current and current responsiveindicator means in said circult. The transmitting means comprises aresistance in said circuit variable in response to a physical conditionexternal to said circuit, said resistance comprising a liquid conductor.

According to the disclosure, the transmitting means preferably comprisesa body of electrically conductive liquid maintained in a substantiallystatic condition, and spaced solid electrical conductors permanentlyimmersed in the body of liquid. One of the conductors immersed in theliquid may be movable responsive to physical pressure external to thecircuit by mechanical means or pressure responsive means including apiston and cylinder, Bourdon tube, bellows or other similar means.Provision is made for compensating for, or minimizing the effect oftemperature variations in certain embodiments.

If the invention is to be used in embodiments wherein it is desired tomaintain the indication constant regardless of variations intemperature, a liquid may be employed which has the characteristic ofminimum change in resistivity with change in temperature. The effect oftemperature in changing resistance of the liquid may also be dealt with,as disclosed, by employing an electrical bridge in the telemeteringcircuit wherein two arms of the bridge are each affected to a likedegree by any change in resistance or conductivity of the liquid so thatthe effect ofsuch change is minimized or nullified.

In order to maintain the body of liquid in a substantially staticcondition, a fluid tight container is provided therefor which iscompletely filled with the liquid, and pressure-compensating means isprovided and designed to be actuated by expansion and contraction of theliquid to maintain the pressure of the liquid within the containersubstantially constant.

-In order to obviate electrolytic decomposition of the liquid and solidconductors, an alternating current source is employed in thetelemetering circuit of the remote indicating system of the invention.

Other objects, advantages and features of novelty will appear as thedescription of the invenelectrical conductor 6 immersed in the liquid 5.Wire 9 connects the other electrical conductor 1 immersed in the liquid5 with the current responsive indicator means 2; and wire l connects theindicator means 2 with the other side of the power source I. Currentflowing through the telemetering circuit including power source i,liquid conductor 5, conductors and I and indicator means 2, causes adeflection of the pointer of said into indicate the correspondingvariations in temtion proceeds in conjunction with the accompanyingdrawings, in which:

Figures 1 to 6 .are diagrammatic views illustrating differentmodifications of the basic concept of the present invention.

Figure 7 is a view illustrating one form of transmitter of the inventionutilizing a Bourdon tube as the pressure responsive means for effectingmovement of the movable conductor member.

Figures 8 and 8A are views illustrating another form of transmitter ofthe invention embodying bellows means as the pressure-responsive meansfor effecting movement of the movable conductor.

Figure 9 is a view illustrating another modification of the transmitterof the invention.

Figure 10 is an isometric view illustrating the application of theinvention to remote indication of airplane control surface position.

The primed reference characters represent corresponding elements in theseveral figures.

The fundamental principles of the invention are illustrated in Figures 1to 6 to which reference is now made in detail. Figure 1 illustrates anembodiment of the invention as a thermometer or external temperatureindicator, and in said figure the numeral i represents a source ofalternating current; 2 indicates a current responsive indicating meter;and 3 generally indicates a transmitting means adapted to sense aphysical condition external to the circuit and to affect the circuit sothat the indicating means 2 will give an indication corresponding to theexternal physical condition desired to be indicated. In Figure l thetransmitting means 3 comprises a container 4 within which is a body ofelectrically conductive liquid 5. Also within the container are thespaced solid electrical conductors 8 and I permanently immersed in theliquid 5. In this embodiment an electrical conductor comprising a wire 8.connects one side of the powe source I with the perature. Examples ofliquids suitable for employment as the liquid body 5 in the embodimentof Figure 1, when the same is utilized as described to function as athermometer, are aqueous solutions of sodiumhydroxide and sulphuric acidas described more fully in the DunmorePatent No. 2,210,903 of August 13,1940.

Another adaptation of the basic concept is illustrated in Figure 2wherein the transmitting means I 5 comprises a container l5 wherein theliquid i1 is preferably a liquid havin a minimum change in resistivityor conductivity with temperature. Spaced electrical conductors H and I8are permanently immersed in the body of liquid ll, the conductor llbeing fixed as to location within the container 16 and the conductor l8being movable within the container it. For the latter purpose theconductor I8 is operatively connected to a pressure responsive means l5.such asabellows of Sylphon or other suitable type, Bourdon tube, or thelike, as shown, Pressure to be measured is applied to the bellows I!through conduit connection 20.

In the operation of the system of Figure 2. pressure applied throughconnection 20 causes movement of the movable conductor 18, changing thelength of the liquid conducting path between the conductors l8 and H,consequently effecting a change in electrical resistance in thetelemetering circuit resulting in a corresponding deflection of thepointer of indicating meter iii. The scale of the indicating meter [3will be calibrated in terms of the pressure to be measured or the factorto be indicated such as, for instance. engine oil pressure, or fuellevel, or the position of one of the aircraft control surfaces, or theposition of the aircraft landing gear, or like factors, the pressureresponsive means l9 being connected through a pressure line with meansactuated by the factor to be indicated.

Figures 3 and 4 illustrate adaptations of the principles of theinvention wherein the transmitting means incorporates two arms of anormally balanced electrical bridge, said two arms being arranged sothat they are equally affected by, and compensate for, changes inapplied voltage and ambient temperatures.

In the system illustrated in Figure 3, the transmitting means 25comprises a container 28 within which the fixed conductors 21 and 2B andthe movable conductor 28 are provided permanently immersed in the bodyof liquid conductor l1, the conductor 28 being movable by means of thepressure responsive mean it. The conductors 2B and 29 are connectedrespectively with oppositesides of the current source through wires IIand 32 respectively. Resistors I3 and 34 are conasoaooa nected in seriesacross the current source and the indicating meter I3 is connected .tothe conductor I! through wire 33 and to a point intermediate theresistors 33 ad 34 by wire 31. It is thus seen that the arrangement oiFigure 3 embodies an electrical bridge in which one arm is formed by theelectrical path through the liquid conductor l1 between the conductors21 and 29; anoth-- er arm is formed by the electrical path through theliquid conductor ll between the conductors 21 and 23; and other arms'areformed respectively by the resistors 33 and 34.

The values of the resistors 33 and 34 are initially selected foraparticular desired in-balance condition of the electrical bridgedepending upon the initial desired positioning of the movable conductor23.

In the operation of the embodiment illustrated in Figure 3, assumingthat the electrical bridge incorporated therein is initially in balance,no current will now from the current source and the pointer of theindicator i3 will remain at its initial zero position. Upon movement ofthe movable conductor 23 from its initial position wherein the bridge isin balance, the length oi. the liquid path between the conductors 28 and21 will be altered so that the effective resistance of the liquidrepresented by the liquid path between the conductors 21 and 23 will becorrespondingly-varied to cause a corresponding deflection cf thepointer of the indicator l3.

Figure 4 discloses a system embodying an electrical bridge in which twoarms thereof are incorporated in the liquid conductor in a mannersimilar to the system of Figure 3. In Figure 4, however, thetransmitting means 40 avails of a construction in which the movableconductor 43 is located between the flxed conductors 4| and 42, saidconductors being permanently immersed in the body of electricallyconducting liquid IT". The movable conductor 43, in this construction,is pivoted at 44 to a link 45 which in turn is pivoted as at 48 to thecontainer 41. A link 43 pivoted to the link 45 is associated with thepressure responsive means IS". The conductor 43 is pendulously suspendedfrom pivot 44 so that the conductor 43 maintains a parallel relation tothe conductors 4i and 42 when the conductor 43 is moved throughactuation of the link 45.

The operation of the embodiment of Figure 4 is substantially comparableto the operation of Figure 3 except that the movable conductor 43 ofFigure 4 is caused to move relative to its initial positioningintermediate the fixed conductors 42 and 4i. The movement of the movableconductor 43 relative to its initial position wherein the bridge is inbalance causes a simultaneous varia tion in the length f the liquid pathbetween the movable conductor 43 and the fixed conductor 4| and in thelength of the liquid path between the movable conductor 43 and the'fixedconductor 42, likewise, to cause corresponding changes in the resistanceof the respective liquid paths resulting in a corresponding deflectionoi the indicator l3".

It will be apparent that in the systems of Figures 3 and 4 any changesin the applied voltage will not ail'ect the bridge balance and anychanges in the resistivity or conductivity of the liquid conductor i1due to temperature variation, or other factors, will equally allect thetwo arms of the bridge which include said liquid conductor I'I'. Thustemperature changes will be compensated for and will not'afiect theoperation oi the system.

The arrangement shown in Figure 5 is similar to Figure 2 except that.instead of the fixed conductor i4 utilized in Figure 2, a bimetalliccon.- ductor I3 is provided in Figure 5 which has one edge fixed to thecontainer Ii as at 52, the element ll being free to bend toward and awayfrom the movable conductor it whenever the electrical conductivity ofthe liquid l'l' is changed due to a change in temperature. Thebimetallic element II is so constructed and arranged that it will bendtoward the conductor i3 and thereby reduce the liquid path between theconductors l3 and 53 when the conductivity oi the liquid is decreasedand the element 50 will bend away from the conductor I8 and thus InFigure 6 the transmitting means 55 is adapted particularly for use as aposition indicator under which condition the movement oi the movable Iconductor 38' relative to the fixed conductor 54 is effected bymechanical operation of a shaft 51 or other type of linkage connected toequipment. whose position is to be indicated, external to thetelemetering circuit including said transmitting means 55. The shaft 31may operate through a liquid-tight packing gland 59. The dial of theindicator 53 will in this case be calibrated in terms 01' thepositioning desired to be indicated, the dial containing suitableindicia indicating the limiting positions, intermediate positions, anddegrees of movement between the limiting positions, as desired.

The current responsive indicator means illustrated may be either of thetype which gives an indication proportional to current or of the typewhich gives an indication proportional to voltage. Necessarily, due tothe particular circuit arrangements, the indicator means 01' Figures 1,2, 5 and 6 will be oi. the former type while the indicator means ofFigures 3 and 4 will be of the latter type. Any suitable indicator meansof these types may be employed as, for instance.

an electrodynamometer oi the type such as is shown in the "Elements ofElectrical Engineering" by Arthur L. Cook, second edition, page 259.'or'a permanent magnet DArsonoval type of direct current instrument suchasillustrated for example in Figure 35, page 47, of the samepublication, with suitable current rectifying means.

It is important to note that the source of current applied in each ofthe telemetering circuits of the remote indicating systems hereindisclosed is an alternating current source. The use of alternatingcurrent avoids electrolytic action on the liquid and solid conductorsand consequent decomposition of the same which would otherwise occur iidirect current were employed in the systems.

While Figures 3 and 4 illustrate the use of a Wheatstone bridgeelectrical circuit it is not intended that the scope of the inventionshall be limited to the specific circuits there illustrated sinceratiometer and potentiometercircuits and various other types ofelectrical bridge circuits may also be used. a

It was mentioned above that when the remote indicating system of theinvention is to be used in applications other than temperatureindicaconductor in the transmitter afiected by ambient temperatures, aliquid conductor should be used which is subject to minimum change inresistivity (or conductivity) with change in temperature; in otherwords, a liquid having a relatively small temperature coefilcient ofchange of conductivity. It is additionally desired to employ a liquidconductor having the following characteristics: a freezing pointsumciently low that said liquid conductor will not freeze at arctictemperatures; a boiling point suflicientiy high that the liquid will notboil at the high temperatures encountered in engine nacelles; stabilityunder operating conditions; freedom from corroslve action; and arelatively small rate of change of viscosity with temperature. Theforegoing characteristics of the liquid conductor are important toinsure stability of operation and accurate indication for the purposesof such applicationsv as in a transmitter for use in a remote indicatingsystem designed to be employed in aircraft for indication of oilpressure or fuel level or indication of the position of aircraftcontrol. surfaces, landing gear position and like ap pllcations.

Liquids embodying the foregoing characteristics,which have been found tobe satisfactory for use as a liquid conductor, comprise high-boilingpoint, low-freezing point, slightly conducting polar organic compoundsof the type of alcohols,

ketones, glycols, glycol ethers, polyglycol ethers, I

sulfones, esters, or other polar organic compounds of the typementioned. Since most of the organic compounds of the type mentioned arecharacteristically 01 low electrical conductivity, it is usuallydesirable to add an electrolyte to such compounds to improve theirconductivity characteristic. Therefore, the liquids which have beenfound to be most satisfactory in use for the purpose of the liquidconductor preferably comprise a polar organic compound of the type mentioned in combination with an organic or inorganic electrolyte which issoluble to a sumcient extent in the liquid.

More specific examples of polar organic compounds of the type mentioned,which have been found to be satisfactory for use as the liquidconductor, include the following: ethyl alcohol, methyl alcohol, propylalcohol, butyl alcohol, ethylene glycol, diethylene glycol, propyleneglycol, hexaethylene glycol, tetraethylene glycol, and otherpolyethylene glycols, methoxy-methory ethanol; ethylene glycol monobutylether having the formula C4HcOCHzCH2OH as for example embodied in thecommercial product marketed under the trade name Butyl Cellosolve;acetone; ethylene glycol monethyl ether having the formula CzHsOCHzCHeOHas for example embodied in the commercial product marketed underv thetrade name Cellosolve.

Electrolytes which have been found satisfactory for use with liquidorganic compounds of the types above mentioned include ammoniumphosphate, potassium phosphate, ethanolamine phosphates, amyl, diamyland triamyl amines, triethanolamine phosphate, butyl amine phosphates,sulfates, chlorides and salts of organic acids. By using varyingquantities of the free acid corresponding to the anion used it ispossible to adjust the pH value and consequently to control the hydrogenion activity to achieve a desired conductivity. Instead of theelectrolytes mentioned, small quantities of water added to the polarorganic solution have been found to improve the operatingcharacteristics of the same weight of the liquid conductor has beenfound to be satisfactory.

To obtain adequate low temperature properties" for the liquid conductor,it is sometimes advantageous to prepare mixtures of two or more of thepolar organic compounds of the types above mentioned since such mixturesusually have a lower freezing point than any of the individualconstituehts.

It will be understood from the foregoing that a satisfactory liquidconductor for the purposes of the invention for use in applicationswhere it is desired not to have the liquid conductor affected by ambienttemperatures may, according to the disclosure herein, comprise a singlepolar organic compound of the type mentioned, alone; or such liquid.conductor may comprise a mixture of two or more of the polar organiccompounds of the type mentioned; or said liquid conductor may compriseone or more of said polar organic compounds in combination with anelectrolyte oi the type mentioned hereinbefore.

It will be understood, of course, that Where an electric bridge circuitis employed incorporating two arms of a normally balanced electricalbridge within the liquid conductor, in such a manner that any change inthe resistance of the liquid conductor affects two arms of the bridge inthe same way, the effects of change in resistance of the liquidconductor due to changes in temperature will be minimized and suchchange in resistance of the liquid conductor will not materially affectthe operation or the system where the arrangement is such that two armsof an electrical bridge are similarly affected by such change inresistance of the liquid conductor. However, it is desirable, even wherethe balanced bridge circuit arrangement is employed, to also use aliquid conductor, having the characteristics above mentioned, tomaintain the current in the meter circuit within the range for which theindicating meter was designed.

Now referring to Figure '7, the embodiment of the transmitter. adaptedfor use in remote indicating systems of the class described, thereshown, comprises a housing 65 within which is mounted the Bourdon tube86, the open end of which is fixed to a hollow post 51, the interior ofwhich constitutes a chamber in communication with the interior ofBourdon tube 86 and also in communication with the fluid pressureconduit 8!, said hollow post 61 being fixed to the housing 85.

Rotatably mounted on a pin 89 secured to the housing 65 is an arm HIcarrying a movable conductor plate "ll movable intermediate the fixedconductor plates 12 and 13. which fixed conductor plates are secured tothe housing 65. The free end of the Bourdon tube is secured to the arm10 as indicated at 14. The movable conductor H is electrically connectedwith the terminal binding post 15 through the arm 10 composed ofconductive material and the lead wire 16. The conductom 12 and II areelectrically connected to the binding posts 11 and II, respectively. bylead wires 18 and 80, respectively. The housing 88 comprises afluid-tight container adapted to be filled with a liquid preferablyhaving the characteristic above mentioned of minimum change inresistivity with change in temperature.

Another embodiment of the transmitter adapted particularly for use inremote indicating systems designed to indicate difierential pressures isillustrated in Figures 8 and 8A. Such transmitters are used, forinstance, in applications such as fuel pressure gages wherein thediiference between the pressure of air introduced to the carburetor andthe pressure of fuel introduced to the carburetor is desired to beindicated. The transmitter illustrated in Figures 8 and 9A comprises ahousing 80 within which are fixed the pressureresponsive elements 8| and82 each of which may comprise a bellows. The interior of the bellows 8|communicates with the pressure conduit 88 and the interior of thebellows 82 communicates with the pressure conduit 84. The bellowsmembers M and 82 are secured to an inner frame generally designated 80adapted to be fixed within the bolls-- ing 80. A beam 80 is pivoted tothe inner frame 85 and is provided with adjusting screws 81 and 88engageable with the inner ends of the'beilows members 8I and 82respectively. The beam 88 has fixed thereto a conductor plate 88positioned intermediate the fixed conductor plates I and I0 I, saidfixed conductor plates being secured to the inner frame 85. Lead wiresI02 and I08 connect the fixed conductor plates with respective contactmembers of a contact plug I04. The movable conductor member 88 iselectrically connected also with a contact member "of said plug I04through electrically conductive elements I05, I09 and I0! and lead wireI08. The housing 80 is provided with a liquid filling opening closed bya screw plug I08, through which opening conductive liquid maybeintroduced into the housing 80 to completely fill the interior thereofimmersing the fixed conductors I00 and MI and the movable conductor 88.

A pair of bellows, only one of which is shown at H0 in Figure 8A, aresecured within the housing 80. The interiors of the bellows members IIOare in communication with the atmosphere through portions the housing80.

In the use of the transmitter illustrated in Figures 8 and 8A, thefluid-tight container 80 is completely filled with conductive liquid andthe conductors 88, I00 and IN connected in a remote indicating circuitsuch as illustrated in Figures 3 or 4. The arrangement may then be usedto remotely indicate differential pressure in an application such as afuel pressure indicator wherein, for instance, one of the conduits 83and 94 may have applied thereto the pressure of air being introducedinto the carburetor and the other of said condults'may have appliedthereto the pressure of fuel being introduced into the carburetor. Inoperation, any change in the differential pressure will cause the beam83 to rock around its pivot III and thus move the conductor plate 88relative to the fixed conductor plates I00 and MI to deflect theindicator such as I3 or I3" of the circuits of Figures 3 or 4. Anychange in physical conditions such as temperature or the like, affectingthe expansion or contraction of the liquid conductor within thecontainer 80 will be compensated for by the provision of the bellows II0 since upon contraction of the liquid within the con- I I0a thereofextending through 8 and 8A. For this purpose tainer 88 the bellows IIIwould be caused to expand by atmospheric pressure or upon expansion ofthe liquid within the container the bellows Ill'will be therebycontracted, so that the liquid pressure within the container 80 ismaintained constant and the container completely filled at all timeswith liquid so that the conductors 88,

I00 and III are always immersed in the liquid' conductor.

Another embodiment of the transmitter is illustrated in Figure 9,comprising a fluid-tight container I20 closed by ascrew cover I2Iprovided with a connection I22 for communication of the'interior of thebellows member I23 with a fiuid conduit, not shown. The bellows elementI 23 is secured to the cover I2I and another bellows element I24 issecured to the opposite end of the container I20. An opening is providedin the container I20 for communication of the interior of the bellowsI24 with the atmosphere. Thi opening, as shown in Figure 9. is normallyclosed by a plug I25. A rod I28 is fixed to the closed ends of thebellows elements I23 facing one another and this rod I28 carries fixedthereto a conductor plate I21 positioned intermediate the fixedconductor plates I28 shown to the container I20. The plates I28 and I28are provided with openings I 28a and I28a of larger diameter than therod I28 to permit the latter to pass through said plates out of contacttherewith. Suitable electrical connections are provided for connectingthe fixed conductor plates I28 and I28 to an external electricalcircuit. Likewise any suitable provision may be made for connecting themovable conductor plate I2I to the external electrical circuit, forinstance, as by means of a lead from said circuit contacting with themetallic fitting I22 conductively associated with the conductor plateI2'I through,

the metallic bellows I23 and rod I26.

In use, the device of Figure 9 may be connected in any suitable electriccircuit such as illustrated by Figure 3 or 4, the container I20completely filled with a liquid conductor, exte'riorly of the bellowselements I23 and I24, and fiuld pressure applied to the interior of thebellows I23 through connecting fitting I22 will cause movement, of theconductor I21 relative to the fixed conductors I28 and I28 to cause thedeflection of the indicator I3 or I3 of Figure 3 or 4. The device ofFigure 9 may be employed to indicate absolute pressure by evacuating thebellows I24 and sealing the same by means of the plug I25. When thetransmitter of Figure 9 is to be used as an oil pressure transmitter,the bellows I24 may be left open to the atmosphere by drilling a smallhole in plug I25. The device of Figure 9 may be used as a differentialpressure transmitter in an application such as that described withreference to Figures V fluid pressure communication may be provided withthe interior of the bellows I24. For example, if the device is to beused as a fuel pressure indicator the pressure of air being introducedto the carburetor may be applied to one of the bellows I23 or I24 andthe pressure of fuel being applied to the carburetor may be applied tothe other of said bellows elements.

It will be apparent that the construction of Figure 9 makes provisionfor compensation for expansion and contraction of the liquid conductorwithin the housing I2I by the employment of the two bellows elementsboth of which are similarly aifected so as to expand or contract uponexpansion or contraction of said'liquid whereby to and I28 secured asmaintain the volume of liquid within the housing I2I constant under allconditions.

Figure 10 illustrates an application of one embodiment of thetransmitter of the invention to the remote indication or the position01! a control surface of an airplane. In Figure 10 a controllable membersuch as an airplane aileron, flap, elevator, or the like, is indicatedat I as being operatively connected by suitable cables or rods I3I to alever I32 fixed on a, shaft I33 connected for rotation through suitablelinks and levers by a joy stick I. A lever I35 is fixed on the shaft I33as is the lever I36. otably connected 9. rod I31 to the opposite end ofwhich is fixed a conductor plate I38 located with in a suitable fluidcontainer I39 adapted to contain a liquid conductor and a fixedconductor plate I40. The conductor plates I38 and ll are connected in aremote indicating electrical circuit such as illustrated by Figures 1 to6 with a power supply and a suitable indicator I iI, through the liquidconductor in the container I39 within which liquid conductor the platesI38 and I40 are immersed. The movement of the control surface I30 by thestick I34 will efiect the movement of the conductor plate I38 relativeto the plate I40 while causing the corresponding deflection oi theindicator III.

From the foregoing it will be seen that the invention provides a remoteindicating-system and a transmitter for employment in such system whichovercome certain disadvantages, hereinbetore mentioned obtaining inprevious types of variable resistance remote indicating systems. Inconnection with the present invention, effects oi. vibration areminimized by the provision of a liquid conductor intermediate themetallic conductors directly interconnected with the telemeteringcircuit in that friction due to metal to metal contacts of resistancemember and contact member is eliminated; and the liquid intermediate themetal conductors operates to dampen vibration which would otherwisecause an unstable condition of the indicating system. Maliunctloning dueto the effects or temperature change are minimized in those applicationswhere it is not desired to have the conductor affected by ambienttemperatures, by the use 01 a liquid conductor having minimum change inresistivity with change in temperature, and also by incorporating twoarms of a balanced electrical bridge within the liquid con ductor sothat both of said arms are equally af-.

fected by the consequences of variations in temperature changingresistivity or conductivity of the liquid conductor. Maliunctioning dueto expansion and contraction of the liquid conductor is obviated by theprovision of compensating means to compensate for such expansion orcontraction.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

i. In a transmitter 01 the class described, in combination, a fluidcontainer adapted to contain a body of electrically conductive liquidtherein, normally spaced electrical conductors in said container andadapted to be immersed in said liquid when the container is filledtherewith, a pair or bellows elements in said container, meansinterconnecting said elements, and means providing communication fromthe interior of one of said elements to the exterior of said container,one of said conductors being secured to said container, and another ofsaid conductors being secured to said first means for movement To thelever I35 is pivrelative to said one of said conductors upon change influid pressure applied to one of said elements.

2. A transmitter as claimed in claim 1, and means alternativelyproviding communication from th interior of the other oi said elementsto the outside or said container or for closing of! such communication.

3. A transmitter as claimed in claim 1, wherein the first meanscomprises a pivoted beam, the ends of which are respectively associatedwith said elements for movement of the beam thereby. 4. A transmitter asclaimed in claim 1, and a bellows elements within said container, theinterior of said last element being in oommunication with theatmosphere, whereby to compensate for expansion and contraction ofliquor within said container to maintain, the pressure of said liquidconstant.

5. In a transmitter oi the class described, in combination, a fluidcontainer adapted to contain a body of electrically conductive liquidtherein, normally-spaced electrical conductors in said container andadapted to be immersed in said liquid when the container is filledtherewith, a pressure responsive element in said container, meansproviding communication from the interior or said element to theexterior of said container to provide a connection for application oi avarying fluid pressure originating outside said container directly tosaid element, one of said conductors being secured to said container,and another of said conductors being operatively secured to saidpressure responsive element for movement relative to said one of saidconductors upon change in fluid pressure applied to said pressureresponsive element.

6. In a transmitter 01 the class described, in combination, a fluidcontainer adapted to contain a body of electrically-conductive liquidtherein, normally-spaced electrical conductors in said container andadapted to be immersed in said liquid when the container is filledtherewith, a pressure responsive element in said container havingrelatively movable opposite end portions, one of said end portions beingsecured to a wall of said container and having a passage therethroughproviding a connection for application of a varying fluid pressure tosaid pressure responsive element, one of said conductors being securedin said container in a stationary position with respect thereto, andanother of said conductors being movably mounted in said container andactuated by the other end portion of said pressure responsive elementfor movement relative to said one of said conductors upon change influid pressure applied to said pressure responsive element.

'7. A transmitter adapted for use in an indicating system, saidtransmitter comprising a container for a body of electrically-conductiveliquid, normally-spaced electrical conductors in said container adaptedfor continuous immersion in said liquid, 8. pair or fluid pressureresponsive elements in said container, means providing a mechanlcalconnection between movable portions of said elements, means providingcommunication from the interior of one of said elements for applicationof a varying fluid pressure thereto, one or said conductors beingsecured in flxed position in said container, and another of saidconductors being connected to said first-named means for movementrelative to said one otsaid conductors upon change in said varying fluidpressure.

other of said conductors being carried by a beam i fuicrunied in saidcontainer, and means connecting each of the fluid pressure responsiveelements to the-beam respectively at opposite sides of the beam fulcrum.

9. A transmitter adapted for use in an indicating system, saidtransmitter comprising a container tor a body of electrically-conductiveliquid, normally-spaced electrical conductors in said container adaptedfor continuous immersion in said liquid, a Bourdon tube in saidcontainer having one end portion secured. to a wall of said container, apassage through said end portion providing a connection for applicationof fluid pressure to said Bourdon tube, one 01 said conductors beingsecured in fixed position in said con tainer and another of saidconductors being movably mounted in said container and actuated by thefree end portion or said Bourdon tube in response to varying fluidpressure applied to said Bourdon tube.

NEUBON W. HARTZ.

